In the production of ammonia (NH3) and urea ((NH2)2CO), a syngas feedstream comprising hydrogen (H2) and carbon monoxide (CO) is first fed to a CO shift unit to convert CO to CO2, before being routed to an acid gas removal facility where the CO2 is separated from the H2. The H2 is then combined with nitrogen (N2) and fed to an ammonia synthesis unit. The CO2 is then combined with a portion of the NH3 product and fed to an urea synthesis unit. The primary reactions of this process are:
3H2+N2xe2x86x922NH3 (ammonia)xe2x80x83xe2x80x83(1)
2NH3+CO2xe2x86x92(NH2)2CO (urea)+H2Oxe2x80x83xe2x80x83(2)
It is known to use gasification to produce the syngas feed to an ammonia/urea production facility. In the gasification process, hydrocarbonaceous material is partially oxidized in the presence of an oxygen rich gas and a temperature moderator at high temperatures. The syngas product of the gasification process primarily comprises H2 and CO. There are many different types of hydrocarbonaceous material that can be fed to a gasification reactor, from natural gas to heavy oils and solid materials such as coal. Because natural gas has a lower C/H ratio than solid and liquid hydrocarbon materials, insufficient CO2 is produced for urea production when a natural gas gasifier is used to produce syngas. Conversely, the high C/H ratio of solid and liquid hydrocarbon materials produces an excess amount of CO2-much more than is needed for urea production-and thus a large portion of the CO2 is vented when only solid and/or liquid hydrocarbon materials are used to produce syngas. Thus, it would be beneficial to develop an integrated gasification and ammonia/urea production process that optimizes the CO2 content of the syngas so as to maximize urea production. Furthermore, CO2 is known to have an adverse effect on the environment, such as contributing to global warming, so it would also be desirable to minimize CO2 venting in an integrated gasification/urea production facility.
The present invention involves a process for the co-production of ammonia and urea in which two parallel gasifiers are utilized so as to optimize the H2/CO2 ratio in the combined syngas product, thereby maximizing the ammonia and urea production. In a first gasifier, solid and/or liquid hydrocarbon materials are partially oxidized in the presence of an oxygen-rich gas in the presence of a temperature moderator, thereby generating a first synthesis gas mixture comprising carbon monoxide, hydrogen and carbon dioxide. The oxygen-rich gas is normally extracted from air through an air separation unit (ASU). The by-product of the ASU, nitrogen (N2), is used in the downstream ammonia production unit.
In a second gasifier, natural gas is partially oxidized in the presence of an oxygen-rich gas, thereby generating a first synthesis gas mixture comprising carbon monoxide, hydrogen and carbon dioxide. By running two gasifiers in parallel on the separate feeds, the feedrates to each gasfier can be independently adjusted to optimize the H2/CO2 ratio in the combined syngas product stream, thus maximizing ammonia and urea production and minimizing CO2 emissions.
The combined syngas product stream is then processed in a CO shift reactor so as to convert any CO in the syngas into H2 and CO2. The CO2 is then removed from the syngas, usually along with H2S and any other sulfur components in an acid gas removal unit, leaving a substantially pure H2 stream. The H2 stream is then combined with N2 from the air separation unit to form ammonia (NH3). The CO2 recovered from a CO2 recovery unit is combined with at least a portion of the NH3 product to form urea ((NH2)2CO).